This assignment is for ETC5521 Assignment 1 by Team goanna comprising of NULL, Emily Sheehan, and Dea Avega Editya.

Soure: Bushfires ravaged Australia

1 Introduction and motivation

The Australian climate is generally hot and dry, which means that most regions can be affected by bushfires at anytime of the year (Australia 2020). Bushfires vary in their magnitude and temperature. Some bushfires can go on for days, weeks or even months. Some bushfires are out of control, while others can be contained.

Last year, the bushfires in Victoria and New South Wales captured the attention of people worldwide. They caused destruction and devastation for several months. Around 33 lives were lost, over 1 billion mammals died, and over 3,000 homes were destroyed (Lisa Richards, Nigel Brew, 2020).

This analysis hopes to understand the relationship between climactic conditions and bushfires, and determine whether climate change has influenced the number of bushfires.

R has been used as the main tool for cleaning and analysis. The analysis proceeds as follows; the data description can be found in section 2, the limitations in section 3, the findings in section 4 and the conclusion is in section 5.

1.1 Research questions

The analysis has been divided into three parts; climactic condition, bushfires and the relationship between climatic condition and bushfires.

Climactic condition:

  • Where does rainfall occur most in Australia? (NEW Q)
  • What is the hottest climate in Australia? (NEW Q)

Bushfires:

  • In which months are bushfires burning?
  • Where are the bushfires burning?

Relationship between climactic condition and bushfires:

  • How does temperature and rainfall affect the number of bushfires?
  • What is the correlation between climactic conditions and bushfires? (NEW Q)

2 Data description

2.1 Australian Fire Data

The Australian fire data has been extracted from the MODIS fire product collection at NASA(NASA 2020). The fire data is collected every five minutes and there are 5101817 observations from 2000-11-01 to 2020-01-05. All the variables in the dataset have been presented in the table below. The variables predominantly used in this analysis are; latitude, longitude and acquisition date.

Table 2.1: Australia fire data
Variable Description
latitude Center of 1km fire pixel but not necessarily the actual location of the fire as one or more fires can be detected within the 1km pixel.
longitude Center of 1km fire pixel but not necessarily the actual location of the fire as one or more fires can be detected within the 1km pixel.
brightness Channel 21/22 brightness temperature of the fire pixel measured in Kelvin.
scan The algorithm produces 1km fire pixels but MODIS pixels get bigger toward the edge of scan. Scan and track reflect actual pixel size.
track The algorithm produces 1km fire pixels but MODIS pixels get bigger toward the edge of scan. Scan and track reflect actual pixel size.
acq_date Date of MODIS acquisition.
act_time Time of acquisition/overpass of the satellite (in UTC).
satellite A = Aqua and T = Terra.
confidence This value is based on a collection of intermediate algorithm quantities used in the detection process. It is intended to help users gauge the quality of individual hotspot/fire pixels. Confidence estimates range between 0 and 100% and are assigned one of the three fire classes (low-confidence fire, nominal-confidence fire, or high-confidence fire).
version Version identifies the collection (e.g. MODIS Collection 6) and source of data processing: Near Real-Time (NRT suffix added to collection) or Standard Processing (collection only). ‘6.0NRT’ - Collection 6 NRT processing.’6.0’ - Collection 6 Standard processing. Find out more on collections and on the differences between FIRMS data sourced from LANCE FIRMS and University of Maryland.
dbright_t31 Channel 31 brightness temperature of the fire pixel measured in Kelvin.
frq Depicts the pixel-integrated fire radiative power in MW (megawatts).
day_night D = Daytime, N = Nighttime

2.2 Climate data

The climate data was extracted from the Australian Bureau of Meterology (BoM). The Bureau of Meterology is the weather station that measures rainfall, wind, temperature, etc.

The cleaned Rainfall data was obtained from from GitHub tidytuesday. It has rainfall for six Australian cities, namely; Perth, Adelaide, Melbourne, Sydney, Brisbane and Canberra. It contains more than 230,000 observations and has been collected from 1858-01-01 to 2020-01-06. There was a few missing values for Brisbane and Canberra. To maintain the integrity of the data the missing values have been added from the source website and cleaned so that the data is complete for Canberra (for 1968-01-01 to 2017-12-31) and Brisbane (for 1893-01-01 to 1998-12-31). Therefore, the rainfall dataset used in this analysis is a combination of the two above.

The temperature data has been retrieved from two sources. The first source for temperature data was GitHub tidytuesday, and it has been collected from 1910-01-01 to 2019-05-31. Since the dates for the cleaned temperature data was not consistent with the fire data, a second source was used. The second source for the temperature data was source website. This data was cleaned to obtain temperatures from 2019-06-01 to 2020-01-05. Both datasets were merged to produce the final dataset used for the analysis. The final dataset has around 530,000 observations taken from 1910-01-01 to 2020-01-05. The seven weather stations chosen were based on the seven Australian cities; Perth, Adelaide, Melbourne, Sydney, Brisbane, Port Lincoln and Canberra.

The structure of the climate data is presented in the table below. The year, city name and rainfall variables were mainly used for from the rainfall dataset and the date, temperature and temperature type were predominantly used from the temperature dataset.

Table 2.2: Temperature data
Variable Class Description
city_name character City Name
date double Date
temperature double Temperature in Celsius
temp_type character Temperature type (min/max daily)
site_name character Actual site/weather station
Table 2.3: Rainfall data
Variable Class Description
station_code character Station Code
city_name character City Name
year double year
month character month
day character day
rainfall double Trainfall in millimeters
period double how many days was it collected across
quality character Certified quality or not
lat double latitude
long double longitude
station_name character Station Name

3 Limitations of analysis

The main limitations of the dataset are concerned with the fire and climate data.

There is no regional division in the fire data. Therefore, the data has been assigned to a state or reigion based on its longitude and latitude, which may lead to location bias in the analysis. (borders for NSW an VIc not easily distinguished)

The rainfall and temperature data has been recorded for some major cities, and the sample is relatively small when compared to the fire data. Therefore, the correlation between the fire and climate data in section 4 may not be precisely accurate as the temperature could be for a city which may be hundreds of kilometres away from the fire it has been correlated to. This may cause a deviation in the results.

4 Analysis and findings

4.1 Climate Conditions

4.1.1 Where does rainfall occur the most in Australia?

4.1.2 When does rainfall occur the most in Australia?

Average monthly rainfall from 2001

Figure 4.1: Average monthly rainfall from 2001

Figure 4.1 finds that the driest months are September, October and May for Australia???

4.1.3 Where is the hottest climate in Australia?

4.2 Bushfires

This section will explore where and what time of year bushfires are burning. Are more bushfires in Summer or Winter? Are bushfires more likely in the Northern Territory?

4.2.1 Which months are bushfires burning?

4.2.2 Have the bushfires been more severe in recent years?

Figure 4.2: The number of Australian fires in 12 month between 2001 and 2020

Figure 4.2 shows some unusual patterns. The trend line for the bushfires in 2019 is very different from other years. This is due to the extensive bushfires in Victoria and New South Wales, which were the biggest bushfires since the European settlement (Nolan et al. 2020).

In September 2011, there was far more bushfires than in any other year in the same period. According to Blanchi et al. (2014), these bushfires were the result of a combination of low rainfall and strong winds.

The overall trend line shows that bushfires are more likely to occur from August to November. This is the winter-spring period in Australia. These months are typically drier as seen in Figure 4.1??(I THINK WE ALSO NEED A GRAPH FOR OVERALL AV RAINFALL TO LINK HERE), which can lead to the ignition of forest fuels (Sullivan et al. 2012) and thus bushfires.

4.2.3 Where are the bushfires burning?

The number of bushfire in different states or regions in the past 20 years

Figure 4.3: The number of bushfire in different states or regions in the past 20 years

Most bushfires occur in the Northern Territory and Queensland, as seen in Figure 4.3. This is likely to both areas being prone to drought and have high concentrations of vegetation.

Figure 4.3 shows that the number of fires in Victoria and New South Wales (NSW) is relatively stable, with the exception of 2019. As mentioned above, this is due to the catastrophic bushfires that took place over this period. Additionally, figure 4.4 shows the distribution of bushfires from the end of 2019 to the beginning of 2020. It predominantly captures Victoria and NSW.

Figure 4.4: The distribution point for Australian bushfires from 2019-12-29 to 2020-01-05(the darker the color, the more serious the fire)

4.3 How does temperature and rainfall affect the number of bushfires?

4.3.1 Positive association with temperature and bushfires

Figure 4.5: Annual average temperature trends from 1910 to 2019, calculated by daily maximum temperature

Figure 4.5 shows the average temperature in 2019 is significantly higher than other years. A strong positive Indian Ocean Dipole (IOD) phenomenon was the culprit(Harris and Lucas 2019), and contributed to very high temperatures and low rainfall across Australia(Meteorology 2019), beginning in May 2019 and lasting until the end of the year.

Indian Ocean Dipole: positive phase. Source from Australian BOM.

Figure 4.6: Indian Ocean Dipole: positive phase. Source from Australian BOM.

How big is the difference between the temperature in 2019 and other years?

Figure 4.7 shows the average annual temperature from 1961 to 1990. From 1910 to mid-1950, the annual average temperature for almost all years was lower than the baseline. Since the mid-1950s, the average annual temperature has been higher than the baseline. Although there has been the odd year, these are outliers.

Moreover, it is worth noting that 2019 is significantly higher than in other years, with a difference of above 1.5°C. As Meteorology (2019) states, 2019 was Australia’s warmest year on record, surpassing the previous record of +1.35°C in 2013.

Evidently, the rising annual temperature has been a warning that Global warming is a growing problem. Ultimately, global warming leads to many natural disasters, bushfires included.

The plot for the difference between the average temperature of 1961-1990(as baseline) and the annual average temperature for each year from 1910 to 2019, calculated by daily maximum temperature

Figure 4.7: The plot for the difference between the average temperature of 1961-1990(as baseline) and the annual average temperature for each year from 1910 to 2019, calculated by daily maximum temperature

Figure 4.8: Annual total fires trends from 2001 to 2019

Figure 4.8 shows the total number of fires in Australia from 2001 to 2019. Compared with Figure 4.5, the total number of fires is fairly consistent??. When the temperature is high, there are generally more fires.

The most fires occurred in 2012 with 474,964 fires, however, the average temperature was relatively low, at 22.57°C. These bushfires can be explained by a lightening strike(Dowdy and Mills 2012).

Ultimately, the analysis above demonstrates that a high temperature is closely related to bushfires. When the temperature is high and climate is dry, forest fuels are more likely to catch alight(G. J. van Oldenborgh et al. 2020).

4.3.2 Negative association with rain and bushfires

Australia’s location means that rainfall is highly variable. It is strongly influenced by the global climate system phenomena such as El Niño, La Niña, and IOD.

Figure 4.9: Annual total rainfall trends from 2001 to 2019

Figure 4.9 shows how the annual rainfall has changed over time in Australia. In 1994 there was a severe drought, influenced by the El Niño weather pattern. This was the fifth year of drought for some parts of Australia(Nicholls 2004). In 2010, the annual rainfall was the highest in 20 years. This was a result of a La Niña event.

2019 was the driest year in the last 20 years. One reason is that the strongest positive IOD reached the highest values on record across 60 years, and due to the frequency and influence of sea-surface temperature changes, the El Nino-Southern Oscillation(ENSO) is neutral throughout the year??????

As a result of the positive IOD, the Walker Circulation was severely curtailed and there was abnormal easterly winds in the Indian Ocean. These winds meant cloud cover in Australia was swept away, dramatically reducing rainfall across Australia(Hughes 2003).

Figure 4.8 shows there has been a consistent average number of fires (250,000) in the last 20 years. The number of fires in 2010 was the lowest, which may be due to the high rainfall as a result of the La Niña event.

From Figure 4.10, the annual average rainfall changed cross-time compare with the average baseline. Over the last 20 years, the rainfall has consistently been below average, with the occasional outlier in 2010 and 2011.

Annual rainfall difference

Figure 4.10: Annual rainfall difference

It is evident that the low rainfall in 2019 was a contributor to the high number of bushfires.

4.3.3 The correlation between climatic conditions and bushfires

The correlation between rainfall, temperature and bushfires

Figure 4.11: The correlation between rainfall, temperature and bushfires

Figure 4.11 demonstrated that rainfall and bushfires have a negative correlation, suggesting that more rainfall means fewer bushfires. Additionally, it shows that a higher temperature leads to more bushfires. Although the correlation between these two variables is small, the relationship is still evident. Moreover, when the temperature is higher, there is less rain.

In conclusion, the main climatic conditions of bushfire is hot and dry(G. J. van Oldenborgh et al. 2020). The graph of annual rainfall and temperature show that the hottest and driest year is 2019, which has the most massive bushfires in Australia as well. Therefore, as the combination of arid and severe hot conditions adds up to more powerful fires, indicating that declines in rainfall and increases in temperature have likely been a primary driver of increases in wildfire area burned.

5 Conclusions

This analysis has looked at when, where and what climactic condition bushfires are likely to thrive in. Bushfires are common from August to November, and are frequently found in the Northern Territory and Western Australia. High temperature and drought are the two biggest contributors to bushfires(G. J. van Oldenborgh et al. 2020). This is consistent with data from 2019, which discovered that it was the hottest and driest year on record with the highest number of bushfires.

Acknowlegments

The authors would like to thank all the contributors to the following R package: Wickham et al. (2019), Wickham (2016), Wickham, Hester, and Francois (2018), Cheng, Karambelkar, and Xie (2019), Ryan and Ulrich (2020), Müller (2017), R Core Team (2020), Arnold (2019), Wickham et al. (2020), Vanderkam et al. (2018), Grolemund and Wickham (2011), Schloerke et al. (2020), Rudis (2020).

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